Study On The Form Transformation And Migration Of Nitrogen And Phosphorus Nutrients Between Multiple Media System In Daihai

Daihai is a typical saline lake in the cold and arid regions of northern China.During the ice-covered period,the lake’s water environment undergoes dramatic changes due to the ice cover.The freezing and salt-exclusion process causes pollutants to accumulate in the sub-ice water,resulting in deteriorated water quality in winter.Studying the migration and transformation of nitrogen and phosphorus nutrients during ice cover formation can help people better understand the eutrophication process of Daihai and provide theoretical guidance and technical support for its water environment management.Therefore,this article investigates the relationship between the forms of nutrients in the ice-water medium and the response of nitrogen and phosphorus nutrients to water environmental factors(water temperature,dissolved oxygen,p H,salinity,conductivity,and ORP)and predicts the changes in lake nutrient levels in the early winter period through the coupling relationship between environmental factors and nitrogen and phosphorus nutrients during the indoor simulation of the freezing process.The main findings of this study are:(1)The nutrient content of Daihai’s water varies seasonally and spatially with changes in water environmental factors.Organic nitrogen accounts for 56% of the main component in various forms of nitrogen,while particulate phosphorus accounts for 68% of the main component in various forms of phosphorus.Organic nitrogen has the highest proportion,accounting for 57%,in various forms of nitrogen in the ice body,while dissolved inorganic phosphorus and particulate phosphorus account for 40% of various forms of phosphorus.p H,water temperature,dissolved oxygen,salinity,and ORP all have an impact on the nutrient content and forms in the water.(2)Laboratory experiments were conducted to simulate the vertical migration process of nutrient salts during the freezing process of Daihai and the impact of various environmental factors on the migration process.After reducing the initial freezing temperature,the distribution coefficients of nutrients between ice and water increased.After reducing the salinity,the capture ability of nitrogen and phosphorus nutrients by the ice body decreased,and the distribution coefficients of various forms of nitrogen and phosphorus in the water all significantly decreased.When the p H was lowered to neutral conditions,the distribution coefficient of nitrogen nutrients decreased significantly,while the distribution coefficient of phosphorus nutrients did not change significantly.(3)Indoor simulation of the freezing process under natural conditions showed that p H first increased and then decreased,while dissolved oxygen,ORP,and conductivity showed fluctuating increases.Changes in water environmental factors had some influence on the distribution of nutrient salts in the ice-water medium during the freezing process.As ice formed,the structure of nutrient salts in the water changed.The proportion of particulate phosphorus in the water decreased,while the proportion of dissolved organic phosphorus increased,and the proportion of ammonia nitrogen decreased,while the proportions of nitrate nitrogen and DON increased.(4)Using the degree-day method to simulate the ice growth process in Daihai in 2022,a multivariate linear regression model was established to describe the relationship between water environmental factors and the growth rate of nutrient salts during the freezing process.By coupling the ice growth model and nutrient salt growth model,the simulation of the nutrient salt variation process during the freezing period was made.The simulation results were close to the actual measurements in 2022,with errors within an acceptable range.According to the simulation results,the trend of nitrogen and phosphorus nutrient salt changes during the ice formation period in Daihai may increase the possibility of algal blooms in the following spring.